The Ground and First Excited Torsional States of Acetic Acid.

A global fit of microwave and millimeter-wave rotational transitions in the ground and first excited torsional states (v(t) = 0 and 1) of acetic acid (CH(3)COOH) is reported, which combines older measurements from the literature with new measurements from Kharkov, Lille, and NIST. The fit uses a model developed initially for acetaldehyde and methanol-type internal rotor molecules. It requires 34 parameters to achieve a unitless weighted standard deviation of 0.84 for a total of 2518 data and includes A- and E-species transitions with J </= 30 and K(a) </= 15. While these results represent a significant improvement over past fitting attempts, it should be cautioned that the present data set is dominated by v(t) = 0 transitions, and no direct infrared measure of the v(t) = 1 <-- 0 torsional interval is available. Copyright 2001 Academic Press.